1. Field of the Invention
This invention relates generally to fabric constructions. It relates in particular to static-dissipating fabrics which are constructed from a non-conducting polymeric web and a conductive substratum bonded thereto.
2. Prior Art Statement
The accumulation of static electricity as a result of the utilization of fabrics is a phenomenon which has commanded the attention of many industries for quite some time. This is easily understood as the presence of static is a cause of considerable annoyance--e.g., items of apparel cling to the body and are attracted to other garments; fine particles of lint and dust are attracted to upholstery and carpet fabrics, increasing the frequency of required cleaning; one experiences a jolt or shock upon touching a metallic object or another person after walking across a carpet or sliding across an upholstered seat. All of these effects are concentrated in atmospheres of low relative humidity.
Of the many existing proposals for preventing the undesirable buildup of static electricity, the most satisfactory, with respect to their efficiency and permanence, appear to be those which comprehend the utilization of fabric constructions wherein some durable electrically-conductive elements (e.g., metal fibers, textile fibers coated with an adhesive matrix comprising electrically-conductive material, or metallic laminate filaments) are present in the fabric, viz., in the face or wear surface of the fabric--i.e., such electrically-conductive elements are positioned so that direct contact thereof with the person is effected as the fabric is utilized. Some of the more noteworthy of these structures are described in U.S. Pat. Nos. 3,678,675; 3,823,035; 3,586,597; 3,706,195; 3,708,335; 3,288,175; 2,302,003; 3,746,573; 3,806,401; 3,836,422; 3,861,429; and 3,955,022; in Belgian Pat. No. 790,254; in Japanese Utility Model, Sho 42-21017; and in Webber, "Metal Fibers," Modern Textiles Magazine, May, 1966, pp. 72-75, among many others.
Notwithstanding the efficacy of these and similar structures, they are all found lacking in one very important aspect, viz, the choice of face or wear surfaces is limited to those materials and structures which can contain the durable electrically-conductive element(s) without substantial adverse effects upon the structural integrity, appearance, and utility thereof--i.e., highly durable face or wear surfaces consisting of dielectric films or sheets of polymeric material such as polyvinyl chloride and polyurethane are excluded. In this regard, the teachings of Webber (U.S. Pat. No. 3,288,175); Cadwell (U.S. Pat. No. 2,302,003); Brinkhoff, et al. (U.S. Pat. No. 3,806,401); and Bischoff (U.S. Pat. No. 3,836,422) are to be especially noted. In view of today's requirements for enhanced product efficiency, durability, and versatility, without any excessive corresponding increases in product costs, such a limitation on the choice of face or wear surfaces is completely undesirable.
References of particular pertinence are set forth below:
1. U.S. Pat. No. 3,042,737 and U.S. Pat. No. 3,582,445 teach the employment of electrically-conductive elements, esp. metal-coated filaments and carbon-coated filaments, respectively, in the wear surface of fabrics having an "open" structure (i.e., pile fabrics such as carpets). Highly durable "closed" wear surfaces such as integral films or sheets of polymeric material, esp. polyvinyl chloride and polyurethane, are not disclosed or suggested. Moreover, the electrically-conductive elements are positioned so that direct contact thereof with the person is effected as the fabrics are utilized (viz, the disclosure and teachings require that conductive elements must be present in the fabric face, not in the backing.)
2. U.S. Pat. No. 3,196,315 discloses a carpet comprising a wear surface and a backing or underlay formed from semiconductive, resilient or sponge-like material having a volume resistivity in the range of 10.sup.3 -10.sup.7 ohms.cm. The comprehended wear surface is an "open" structure, (cf. (1) above), and the underlay in its preferred embodiment is a sponge rubber or like structure having electrically-conductive carbon particles dispersed therein. Employing the teachings of this reference, an 18 oz./yd.sup.2 cut pile carpet was constructed from bulked continuous filament nylon 6 carpet yarn comprising 136 individual strands and having a total denier of 2600. This nylon carpet yarn was tufted into an underlay comprising woven polypropylene having 1 gm/yd.sup.2 of the electrically-conductive fiber described and claimed in U.S. Pat. No. 3,823,035, the underlay having a volume resistivity within the range 10.sup.3 -10.sup.7 ohms.cm. The static level of this carpet was determined by standard means (see, e.g., the "Static Electricity Test" described in U.S. Pat. No. 3,823,035 in Col. 8 at line 17 ff.) and was found to be 6.5 kilovolts. Although this value represents an improvement over similar nylon carpets having no conductive underlay (which carpets provide static levels of 12 to 13 kilovolts), static was not reduced below the threshold level of human sensitivity (which is universally accepted as 2.5 to 3.5 kilovolts, as in well known to those of skill in the art). As a consequence, it is clear that U.S. Pat. No. 3,196,315 does not teach one of skill in the art how to prepare static-dissipating fabric constructions which are capable of preventing the buildup of static to levels exceeding the threshold level of human sensitivity.